EP1915519B1 - Exhaust pipe - Google Patents

Abstract

The invention relates to an exhaust pipe (20) comprising the following elements which are disposed concentrically, namely: an inner tube which is made from an inorganic matrix composite (22); an outer metal tube (24); and a support layer (26) which is made from a fibrous material. The thickness of the support layer (26) measures between 2 mm and 10 mm and preferably between 3 mm and 6 mm. The maximum support pressure exerted by the support layer (26) on the inner tube (22) is between 10-4 MPa and 10-1 MPa.

Description

• un tube interne en composite à matrice inorganique ;
• un tube externe métallique ; et
• une couche de maintien d'un matériau fibreux.

The present invention relates to an exhaust duct comprising, arranged concentrically:

• an inner tube of inorganic matrix composite;
• a metal outer tube; and
• a layer for holding a fibrous material.

Nowadays, the implementation of pollution control components in the exhaust lines requires precise management of the thermal flows of the engine to the exhaust outlet. In particular, it is necessary to allow most of the heat produced by the engine to reach the pollution control equipment located on the exhaust line. Such a transfer is required especially when starting the vehicle to allow a rapid rise in temperature of the catalytic elements. Indeed, before a predetermined temperature, they are not active.

In order to allow a rapid rise in temperature of the catalyst, it is known that the elements of the exhaust line between the engine outlet and the pollution control members comprise an inner ceramic tube surrounded by an outer tube of metal between which is interposed an insulating material. Indeed, the ceramic tube, because of its low thermal inertia, greatly reduces the heat transfer of the exhaust gas to the ceramic tube.

Furthermore, the low thermal expansion of the inner ceramic tube makes it possible to produce monobloc internal pipes even for engines that release exhaust gases at very high temperatures, in particular greater than 1000.degree. C. without risk of thermomechanical rupture.

Such a structure is used in particular in the exhaust manifolds provided immediately at the output of the engine.

Such a collector is described for example in the document US 6,725,656 B2 .

In this document, it is proposed to provide between the dense inner ceramic tube and the outer metal tube, a relatively thick, thermally insulating layer of ceramic fibers in contact with the ceramic tube. The thick layer of ceramic fibers has a thickness of between 1 mm and 40 mm and preferably between 2 mm and 20 mm.

In a particular embodiment, a so-called thin layer of stress isolation is provided between the thick layer of ceramic fibers and the outer tube of metal. This thin layer of stress isolation is between 0.05 mm and 2 mm and preferably between 0.1 mm and 0.5 mm. This layer of stress insulation is designed to absorb the vibrations of the engine and the road to prevent the destruction of the thick ceramic fiber layer. This layer also attenuates the vibrations, in particular by compensating the differential thermal expansions between the layer of thick ceramic fibers and the outer tube of metal during the heating of the exhaust line. Indeed, when the inner tube is traversed by gases at high temperatures, there are significant differential thermal expansions because the dense inner ceramic tube and the thick layer of ceramic fibers have relatively low expansion coefficients in comparison with the outer tube made of metal.

This thin layer of stress isolation is necessary in the device described in US 6,725,656 B2 because the thick layer of ceramic fibers does not have the properties required to compensate for the clearance due to the differential expansion between the dense ceramic inner tube and the outer metal tube.

US 6,725,656 B2 thus describes a multilayer structure comprising at least a dense ceramic inner layer, a thermally insulating thick layer of ceramic fibers and a metal layer. This structure is optionally supplemented by a thin layer of stress insulation for protecting the thick layer of ceramic fibers from vibrations.

However, in addition to vibrations that may damage the thick layer of ceramic fibers, a structure of the type described in US 6,725,656 B2 is still subject, at the inner wall of the dense ceramic inner tube, to stresses due to the flow of exhaust gas. These stresses tend to cause the inner tube with the flow of gas causing a problem of maintaining the inner ceramic tube in the outer metal tube.

However, the teaching of US 6,725,656 B2 contains no element capable of solving the problem of maintaining the dense ceramic inner layer in a metal structure.

Therefore, an object of the invention is an exhaust duct for satisfactory heat delivery comprising an inorganic matrix composite inner pipe held in an outer metal structure.

For this purpose, the subject of the invention is an exhaust duct of the aforementioned type, characterized in that the thickness of the holding layer is between 2 mm and 10 mm, and preferably between 3 mm and 6 mm, and in that the minimum holding pressure exerted by the holding layer on the inner tube is between 10 ^-4 MPa and 10 ^-1 MPa.

• la pression de maintien minimale exercée par la couche de maintien sur le tube interne est comprise entre 10^-3 MPa et 5.10^-2 MPa,
• le tube externe métallique a une épaisseur comprise entre 0,5 mm et 3 mm,
• le tube externe métallique est choisi dans le groupe consistant en un tube d'acier, un tube d'aluminium et un tube de titane,
• le tube externe est formé de deux demi-coquilles en forme de gouttières assemblées par des joints longitudinaux,
• le tube interne en composite à matrice inorganique a une épaisseur inférieure à 2 mm,
• le tube interne composite à matrice inorganique comprend une matrice constituée par au moins un polymère inorganique,
• le polymère inorganique est un géopolymère à base d'aluminosilicate,
• le tube interne composite à matrice inorganique comprend une matrice renforcée par des fibres, notamment à base de carbure de silicium (SiC), de carbone, de silice (Si02), ou d'un fil métallique inoxydable résistant à des températures égales ou supérieures à 600°,
• la couche de maintien comprend une nappe de fibres de céramique,
• la couche de maintien comprend des fibres de céramique et un liant inorganique, la couche de maintien comprenant entre 90 % à 100 % en poids de fibres céramiques,
• les fibres céramiques sont des fibres sélectionnées dans le groupe consistant en des fibres de silice, de fibres d'alumine, de fibres de zirconium, de fibres d'alumine-borosilicate; et de mélanges de celles-ci,
• les fibres contenues dans la couche de maintien sont un mélange de fibres d'alumine et de fibres de silice dans un rapport de respectivement 72 et 28 %,
• la GBD du matériau constituant la couche de maintien est comprise entre 0,1 et 0,6,
• la densité du matériau constituant la couche de maintien est comprise entre 500 g/m² et 3000 g/m²,
• le coefficient de frottement du matériau formant la couche de maintien contre les surfaces des tubes interne et externe est compris entre 0,15 et 0,7, et
• le collecteur d'échappement comporte au moins un conduit d'échappement tel que défini ci-dessus.

According to particular embodiments, the following path includes one or more of the following characteristics:

• the minimum holding pressure exerted by the retaining layer on the inner tube is between 10 ^-3 MPa and 5.10 ^-2 MPa,
• the outer metal tube has a thickness of between 0.5 mm and 3 mm,
• the outer metal tube is selected from the group consisting of a steel tube, an aluminum tube and a titanium tube,
• the outer tube is formed of two half-shells in the form of gutters assembled by longitudinal joints,
• the inorganic matrix composite inner tube has a thickness of less than 2 mm,
• the inorganic matrix composite inner tube comprises a matrix consisting of at least one inorganic polymer,
• the inorganic polymer is a geopolymer based on aluminosilicate,
• the inorganic matrix composite inner tube comprises a matrix reinforced with fibers, in particular based on silicon carbide (SiC), carbon, silica (SiO2), or a stainless wire resistant to temperatures of 600 ° and above,
• the holding layer comprises a layer of ceramic fibers,
• the holding layer comprises ceramic fibers and an inorganic binder, the holding layer comprising between 90% to 100% by weight of ceramic fibers,
• the ceramic fibers are fibers selected from the group consisting of silica fibers, alumina fibers, zirconium fibers, alumina-borosilicate fibers; and mixtures thereof,
• the fibers contained in the holding layer are a mixture of alumina fibers and silica fibers in a ratio of 72 and 28% respectively,
• the GBD of the material constituting the holding layer is between 0.1 and 0.6,
• the density of the material constituting the holding layer is between 500 g / m ² and 3000 g / m ² ,
• the coefficient of friction of the material forming the holding layer against the surfaces of the inner and outer tubes is between 0.15 and 0.7, and
• the exhaust manifold comprises at least one exhaust duct as defined above.

• la figure 1 est une vue en perspective d'un collecteur d'échappement selon l'invention ; et
• la figure 2 est une vue en section d'un conduit d'échappement du collecteur de la figure 1.

The invention will be better understood on reading the description which follows, given solely by way of example and with reference to the drawings in which:

• the figure 1 is a perspective view of an exhaust manifold according to the invention; and
• the figure 2 is a sectional view of an exhaust duct of the collector of the figure 1 .

The exhaust manifold 10 illustrated on the figure 1 is intended to be disposed at the output of a heat engine at the entrance of an exhaust line of a motor vehicle. This exhaust line comprises downstream of the manifold 10, possibly a supercharging system (turbo) and one or more depollution elements capable of operating at high temperature.

The collector 10 has a plurality of inlets 12 converging towards an outlet flange 14. The inlets 12 are connected to the outlet flange 14 by ducts 20 opening into each other.

As illustrated on the figure 2 each conduit 20 comprises an inner tube 22 of inorganic matrix composite, in particular ceramic, and an outer metal tube 24 between which is disposed a holding layer 26 made of a ceramic fibrous material.

Preferably, the conduit consists of only three layers 22, 24 and 26.

The outer tube 24 is formed of a metal wall having a thickness of between 0.5 and 3 mm. According to a first embodiment, the outer tube 24 is a cylindrical metal tube including steel, aluminum or titanium.

Alternatively, and as illustrated on the figure 1 , the outer tube 24 is formed of two metal half-shells 27 in the form of gutters joined by opposite longitudinal joints 28.

At each of its ends, the outer tube 24 is provided with flanges allowing its connection with, upstream, the engine and downstream, the exhaust line of the vehicle.

The choice of a metal outer tube is justified by the need to ensure optimum sealing upstream of the pollution control elements, and in particular at the junction of the outer tube with the upstream and downstream metal flanges. As an indication, the authorized leakage flow rate is 25 liters / hour, at 20 ° C. under 1.3 bars. The inner tube 22 is a tube formed from an inorganic matrix composite material, in particular a ceramic material. Examples of inorganic matrix composite materials capable of forming the inner tube 22 are given in the patent applications US6134881 and W02004106705 . These materials are formed by the combination of a matrix consisting of at least one inorganic polymer, preferably of geopolymer type, based on aluminosilicate. This matrix is reinforced by fibers, in particular based on silicon carbide (SiC) or carbon or silica (SiO2), or even a stainless wire resistant to temperatures of 600 ° C or higher (stainless steel, inconel®, ...). Preferably, the inner tube 22 is formed of a wall having a thickness of less than 2 mm.

The holding layer 26 has a thickness of between 2 and 10 mm. It is preferably between 3 and 6 mm.

The holding layer 26 is formed of a layer of ceramic fibers, especially long ceramic fibers preferably associated with an organic binder and / or inorganic.

The organic binder is only useful when placing the holding layer around the inner tube; it is consumed during the first temperature rise of the exhaust duct on the vehicle. This binder represents from 0 to 15% by weight of the new holding layer.

The inorganic binder is used when it is necessary to ensure better cohesion between the fibers during operation of the vehicle and must not be burned. This binder represents from 0 to 10% by weight of the organic binder-free holding layer.

Thus, in the operating configuration, the ceramic fibers represent 90 to 100% by weight of the holding layer, the remainder being the inorganic binder.

The ceramic fibers present in the holding layer 26 are selected from the group consisting of silica fibers, alumina fibers, zirconium fibers, borosilicate alumina fibers and a mixture thereof. The sheets may be needled, which improves their behavior over time.

Preferably, the fibers used are mullite fibers combining alumina and silica in a ratio of 72% and 28%, respectively.

The density of the material constituting the holding layer is between 500 g / m ² and 3000 g / m ² .

This holding layer 26 must maintain the inner tube 22 in the outer tube 24 regardless of the operating conditions.

Depending on the characteristics of the inner ceramic tube and the nature of the holding layer (mass, contact surface with the holding layer), the maximum acceleration to which it is subjected and the maximum flow and pressure of the exhaust gas, the minimum pressure to be applied to maintain said inner tube in the metal tube is determined. This minimum pressure takes into account, in addition to the above mentioned solicitations, a specific corrective factor of the operating behavior of the inner ceramic tube and the holding layer. A coefficient of friction intervenes in this corrective factor. Depending on the material constituting the inner and outer tubes, the material constituting the holding layer is chosen so that the coefficient of friction of the damping layer against the surfaces of the inner and outer tubes is between 0.15 and 0.7. The minimum holding pressure is between 10 ^-4 and 10 ^-1 MPa and preferably between 10 ^-3 MPa and 5.10 ^-2 MPa.

The value of 10 ^-3 MPa corresponds to an inner tube of 100 grams having a contact area of 40 dm ² with the holding layer subjected to an acceleration of 10 g and a pressure drop of 100 Pa. This pressure drop is induced by the friction of the gases against the wall of the inner tube. The value of 5.10 ^-2 MPa corresponds to an internal tube of 200 grams having a contact surface of 20 dm ² with the holding layer and subjected to an acceleration of 40 g and a pressure drop of 250 Pa.

It has been found that, depending on the type of sheet chosen to constitute the holding layer 26, it is necessary, on the one hand, to prevent the destruction of the fibers constituting the sheet and, on the other hand, to avoid damaging the sheet. inner tube of inorganic matrix composite. For this, it is essential not to exceed a certain pressure exerted on the inner tube and therefore a certain compression of the web: this maximum pressure is between 0.1 and 1 MPa and preferably between 0.3 and 0.7. MPa.

GBD (Gap Bulk Density) is the ratio between the density in kilograms per square meter of the chosen layer to form the support layer and the clearance in millimeters between the outer and inner tubes. Density is a characteristic of the tablecloth. In the context of the invention, the value of the clearance between the outer and inner tubes is dictated in particular by the shape constraints of the exhaust line element. The usable GBD range is 0.1 to 0.6. The minimum value is given to avoid vibrational deterioration of the fibers, the maximum value is given to avoid the deterioration of fibers by compression.

The relationship between the GBD and the pressure P exerted on the inner tube by the holding layer is given, for a sheet made of long ceramic fibers, by an equation of the P = A type. (GBD) ³ + B. (GBD) ² + C (GBD) + D.

When choosing a sheet of specific density intended to maintain the inner tube separated from the outer tube by a given clearance, it is ensured that the pressure exerted will be greater than the minimum holding pressure and less than the maximum pressure supported. by the fibers and the inner tube. It is still necessary to take into account that, in use, the clearance between the inner tube and the outer tube may vary by plus or minus 1 mm due to the differential expansion between the inner tube and the outer tube.

Thus, for a holding layer 26 formed from a sheet made of long ceramic fibers with a density of 900 g / m ² , placed between an inner tube (composite pipe of 200 grams having a contact area of 20 dm ² with the holding ply and subjected to an acceleration of 40g) and an outer tube separated by a minimum play of 3 mm, the GBD is 0.3. The holding pressure exerted by the ply on the internal ceramic matrix composite tube is then, for the chosen type of ply, 0.2 MPa. This GBD of 0.3 is well within the recommended range of GBD.This pressure is greater than the minimum holding pressure calculated for this application (5.10 ^-2 MPa) and lower than the mechanical strength of the inner tube.

The maximum clearance for this same application is 4.25 mm, corresponding to a GBD of 0.22 and a holding pressure of 6.10 ^-2 MPa. The GBD remains within the range of use of the web and the induced pressure remains above the minimum holding pressure.

It is noted that with such an exhaust duct, the holding material correctly ensures the maintenance of the inner tube of inorganic matrix composite in the outer metal tube regardless of the temperature of the exhaust line and the flow conditions. gaseous and acceleration to which the inner tube is subjected without deteriorating or damaging the inner tube.

Claims (17)

1. Exhaust conduit (20) comprising the following arranged concentrically:

   • an inner tube made of a composite with an inorganic matrix (22);

   • an outer metal tube (24);

   • a holding layer (26) made of a fibrous material;

   wherein the thickness of the holding layer (26) lies in the range of between 2 mm and 10 mm, preferably between 3 mm and 6 mm, characterised in that the minimum holding pressure exerted by the holding layer (26) on the inner tube (22) lies in the range of between 10^-4 MPa and 10^-1MPa.
2. Conduit according to claim 1, characterised in that the minimum holding pressure exerted by the holding layer (26) on the inner tube (22) lies in the range of between 10^-3 MPa and 5.10^-2 MPa.
3. Conduit according to any one of the preceding claims, characterised in that the outer metal tube (24) has a thickness in the range of 0.5 mm and 3 mm.
4. Conduit according to any one of the preceding claims, characterised in that the outer metal tube (24) is selected from the group comprising a steel tube, an aluminium tube and a titanium tube.
5. Conduit according to any one of the preceding claims, characterised in that the outer tube (24) is formed from two half-shells (27) in the form of channels joined together by longitudinal joints (28).
6. Conduit according to any one of the preceding claims, characterised in that the inner tube made of composite material with an inorganic matrix (22) has a thickness of less than 2 mm.
7. Conduit according to any one of the preceding claims, characterised in that the inner tube made of composite material with an inorganic matrix (22) contains a matrix formed by at least one inorganic polymer.
8. Conduit according to claim 7, characterised in that the inorganic polymer is an alumino-silicate-based geopolymer.
9. Conduit according to any one of the preceding claims, characterised in that the inner tube made of a composite material with an inorganic matrix (22) contains a matrix reinforced by fibres, in particular based on silicon carbide (SiC), carbon, silicon dioxide (SiO₂) or a non-oxidising metal wire resistant to temperatures equal to or higher than 600°.
10. Conduit according to any one of the preceding claims, characterised in that the holding layer (26) comprises a layer of ceramic fibres.
11. Conduit according to any one of the preceding claims, characterised in that the holding layer (26) comprises ceramic fibres and an inorganic binder, wherein the holding layer contains between 90% and 100% by wt. of ceramic fibres.
12. Conduit according to claim 11, characterised in that the ceramic fibres are fibres selected from the group comprising silicon dioxide fibres, aluminium fibres, zirconium fibres, alumino-borosilicate fibres and mixtures thereof.
13. Conduit according to claim 12, characterised in that the fibres contained in the holding layer (26) are a mixture of aluminium fibres and silicon dioxide fibres in a ratio of 72 and 28% respectively.
14. Conduit according to any one of the preceding claims, characterised in that the GBD of the material forming the holding layer (26) is in the range of between 0.1 and 0.6.
15. Conduit according to any one of the preceding claims, characterised in that the density of the material forming the holding layer (26) is in the range of between 500 g/m² and 3000 g/m² _.
16. Conduit according to any one of the preceding claims, characterised in that the coefficient of friction of the material forming the holding layer (26) against the surfaces of the inner tube (22) and outer tube (24) is between 0.15 and 0.7.
17. Exhaust manifold (10) comprising at least one exhaust conduit (20) according to any one of the preceding claims.

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